Returns a data.frame summarizing every built-in vector and raster tile provider,
whether it uses WebGL vector tiles (vector_gl) or XYZ raster tiles (raster_xyz),
whether an API key is required or optional, and the environment variable name.
Returns a data.frame summarizing every built-in vector and raster tile provider,
whether it uses WebGL vector tiles (vector_gl) or XYZ raster tiles (raster_xyz),
whether an API key is required or optional, and the environment variable name.